“Your genes load
the gun. Your lifestyle pulls the
trigger.”
--Mehmet Oz
Genetic expression is the outcome of millions of connections
between genetic factors. The Human Genome Project, substantially final by 2003,
showed that the differences in DNA between people are just 0.1 percent:
one-tenth of a single percentage. We are
a single species and anyone who is human shares 99.9% of DNA with every other
human. So any two people are 99.9%
identical genetically – from any place or group on the planet.
Chimps, our closest biological relatives, share just
5.2-6.2% for the entire genome. Although
humans are primates in the great apes line, our last common ancestor lived 6 to
8 million years ago. The first four
million years of our history were lived out exclusively in Africa. Charles Darwin proposed this origin theory in
1871 but at the time this was considered a wild guess—while now richly
confirmed by fossil as well as genetic evidence (Smithsonian Museum of Natural
History).
But what about the differences? Height, weight, face shape, body build, skin
and eye color, hair texture, and straight, wavy, or curly hair are visible
outward expression (phenotypes). Susceptibility
to heritable disease like autism and schizophrenia, cancer, Type II diabetes, cystic
fibrosis, and heart disease, along with the physical body factors, are all very
marginal factors compared to what is shared.
Malarial resistance is traceable to the genetic lack of the Duffy
antigen in the red blood cell, protecting two-thirds of the African population
from the disease over thousands of years.
But the differences are what allow us to associate a single difference
with large groups, and that is where our attention—which is a cultural
artifact—is focused. The human
propensity to compare visible aspects between people is acute and has survival
origins, as for example in our keen ability to tell faces apart, even very
closely related ones. This highly developed skill, unique to humans, is one which
we rarely think about as a brain tool--except whenever we fail to recognize
someone we should-- is located in the fusiform gyrus, which so far appears to
be dedicated to this single operation.
Gender is the leading biological difference between
people. On the gender side, human births
show a ratio bias toward boys – 105 male births versus 100 for girls. One explanation for this off-balance is that
fewer males live to adulthood, so the male imbalance levels off
eventually. We focus on gender, though,
not because it is a biological reality, but because such a rich heritage of
meaning and behavior has been built up around the male / female binary difference. Gender has greater cultural weight than aa
simple biological category.
Each individual has a total of 20,000 to 25,000 genes. But there are 3 billion base pairs within the
species, which means that any pair of humans differs by 3 million. With 3 billion DNA letters in the human
genome, sequencing them is among the most ambitious science project of all
time, along with splitting the atom. The
HGP is the standard for all research in this arena. As change expert Virginia Satir has noted, a surgeon
can go anywhere on earth and operate on any person at all; we are that
standardized physically. Now we have a far
finer-tuned standard, the blueprint based on molecular-scale reality explaining
what makes us both different--and the same.
Within any species, genetic variation
can result from several sources. Mutations,
the changes in the sequences of genes in DNA, are one source of genetic variation—without
them, genetic evolution would not be possible. Gene
flow, another source, is the movement of genes between
different groups, along with our long history of mobility across land and
water. Sexual reproduction leads to the
creation of new combinations of genes (National Geographic Resource
Library).
Genetic changes over time can trace
human origins, development, and mobility. Genomics is the study of individual
genome and gene interactions along with the effects of environmental factors
(and fitness outcomes). Our
homogeneity indicates a young species—less than a quarter million years old for
modern humans. Individuals from widely separated groups can be more similar
than individuals from the same group, which is why the concept of race is
without scientific basis. The widest difference
between groups is actually found in Africa, giving credence to the African
origin hypothesis, in which a subset of that continent’s population moved out
60,000 years ago to populate the earth. Meanwhile the African genetic story has maintained
the oldest genome, which continued to generate variations leading to modern
distinctions between groups.
Natural selection made possible by genetics favors some
genes over others as more survival-friendly, including cultural values-based
biases that select for some traits (like height or health) over others. So the genome, too, has a bias—it tends
toward better survivability over time and across generations. (The peppered moth
wing color, from light to dark, being the classic example of selection for survival
in industrial Manchester.) Whatever our
genetics, it is finally culture and its selective values, or positive bias,
that “pulls the trigger” on how genetic expression operates as a social
force. This means that it is culture,
not biology, that determines what genetic variations mean to our thought and
action—whether advantageous or detrimental.
Photo: Pixabay
